What are asphalt shingles?
Asphalt shingles (also called bitumen or felt shingles) are small, flat roofing units laid in overlapping courses on a pitched roof. They consist of a glass fibre mat coated with bitumen on both sides and surfaced with slate or mineral granules. In the Netherlands they are simply called shingles. They are light, affordable and easy to handle, which makes them popular on garden buildings, log cabins, carports and extensions.
Types
- Asphalt shingles: rectangular, hexagonal or beaver-tail patterns in many colours. A self-sealing strip on the underside bonds to the course below once warmed by the sun
- Wood shingles: sawn, often from western red cedar. Not to be confused with shakes, which are split and have a rougher face
Application and installation
Asphalt shingles are not self-supporting and need a solid roof deck: OSB, plywood or tongue-and-groove boards. Key points:
- Roof pitch. Always follow the manufacturer. The minimum pitch is typically around 15°; on shallow pitches (roughly 15 to 25°) manufacturers require a full bitumen underlay. Below the minimum, water sits on the roof and leaks follow
- Underlay. Lay an underlay over the whole deck, with extra strips in valleys and along the edges
- Nailing. Use galvanised or stainless steel roofing nails, typically 4 per shingle on the marked nailing line, and more on very steep roofs. Do not nail too high (the shingle tears or lifts) or too low (the nail shows and leaks). Nails must be covered by the next course
- Starter course. Begin at the eaves with a starter strip so the joints of the first course are also watertight
- Ventilation. On an insulated roof, provide a ventilated void below the deck, with intake at the eaves and exhaust at the ridge
Common mistakes
- Laying in cold weather. The sealing strip only bonds once the sun warms the roof, and cold shingles become stiff and brittle. Lay in mild weather where possible or follow the manufacturer’s cold-weather advice (often extra adhesive dabs)
- Not mixing bundles while laying, so colour differences between batches show as patches on the roof
- A thin or damp deck, in which nails do not hold or which starts to ripple
Related terms
- Roof decking
- OSB board
- Bitumen
- Roof pitch
- Roof covering
- Diamond shingle roofing
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